Project Summary: The goal of this research is to bridge the gap between synaptic function and the control of behavior by identifying the signaling pathways that control synaptic activity. Our studies of the model organism C. elegans have shown that the integrated activities of 3 major Ga pathways control synaptic activity to produce the locomotion behavior. Within this synaptic signaling network, the neuronal Gccs pathway is an especially critical but poorly understood link between synaptic function and behavior. Despite years of research in multiple model organisms, we do not understand why animals lacking a neuronal Gas pathway are paralyzed. This proposal takes 3 approaches to investigate the core purpose of the neuronal Gas pathway during the execution of behaviors. Aim 1 asks whether and how the Gas pathway affects various synaptic vesicle pools, including a newly discovered pool of membrane contacting vesicles next to the active zone. Aim 2 expands on our startling discovery that high energy light transforms paralyzed mutants lacking a neuronal Gas pathway into hyperactive animals with coordinated locomotion. Our genetic analysis suggests that high energy light activates a pathway that bisects the network downstream of the Gas pathway but upstream of the synaptic vesicle priming machinery. Through a large forward genetic screen, we have isolated 21 Lite mutants defective in this response. We propose to use these mutants to investigate the molecular basis of the presynaptic light response, and thus obtain clues about the molecular targets of the UNC-31/ Gs pathway. Aims 3 and 4 use forward genetic approaches to identify the signals that control activation of the neuronal Gas pathway. To investigate the mutants in Aims 2-4, we first map the mutation and identify the gene that is mutated. We then apply a set of strategies, including genetic pathway analysis, site-of-action studies, electrophysiological and behavioral assays, and immunolocalization experiments, to determine the specific role of each protein in the network. Relevance: The pathways of the synaptic signaling network are found in all animals, from worms to humans. Studies in model organisms such as worms and flies suggest that all behavior, learning, and memory formation occurs through the pathways of this network. However, the connection between the synaptic signaling network pathways and the control of behavior remains unclear. The experiments in this proposal will drive the discovery of critical missing links that are necessary to decipher the underlying logic of the network. Basic insights from our research should provide important clues and drug targets for human neural disorders such as behavioral and psychiatric disorders, depression, hyperactivity, and memory disorders.